1. Field of the Invention
The present invention relates to a keyboard including a key matrix, a radiation emitter for each column of keys, a radiation receiver for each line of keys, means disposed at each intersection of a column and a line for deflecting the radation from the corresponding emitter to the corresponding receiver, means controlled by each key for interrupting the radiation of the corresponding emitter and means for controlling the emitters sequentially and cyclically.
With such a keyboard, alphanumeric data can be fed in manually into a word processing machine, a computer, or a terminal connected to a telecommunications network for example.
2. Description of the Prior Art
Such a keyboard is already known, described in U.S. Pat. No. 4,417,824. In this keyboard, the radiation considered is light radiation, each column includes a first light guide made from a transparent material having an index greater than that of air, inside which the light emitted by the corresponding emitter propagates and each line includes a second light guide made from the same material as the first guide and inside which light received by the corresponding receiver propagates. Each means for deflecting the radiation from an emitter to a receiver includes, in the first guide, or emission guide, two reflecting surfaces for causing a part of the light emitted to leave the emission guide in a direction parallel to that of the second guide and, in the reception guide, a reflecting surface for causing the light leaving the emission guide to enter. Each interruption means includes an opaque flap which is interposed between the emission guide and the reception guide for interrupting the light radiation.
Such a keyboard has several drawbacks. First of all, since the transparent material used for the guides is not perfect, the light propagates therein with attenuation. In addition, in order to be deflected, the radiation from the emitter undergoes three reflections. Moreover, in order to enter then leave the emission guide this radiation must cross an air-transparent medium interface then a transparent medium-air interface. The same goes for entering then leaving the reception guide. Now, each reflection or interface passage gives rise to light energy losses. Thus, after propagation, reflections and interface crossings, the light portion emitted by an emitter which is received by a receiver is relatively small. This reduces the operating reliability of the keyboard and requires the use of powerful sources and sensitive sensors. Furthermore, the use and positioning of emission guides having a relatively complex shape increase the manufacturing costs.
The European application No. 0 151 022 describes a matrix keyboard including a light emitter per column and a receiver per line and means for controlling the emitters sequentially and cyclically. In this keyboard, the light propagates in air, inside hollow and rectilinear channels corresponding to the columns and to the lines. Such a keyboard has then none of the above drawbacks. However, since the light propagates in a straight line, and since the columns are substantially perpendicular to the lines, it is not possible to use, as in U.S. Pat. No. 4,417,824, keys each controlling a single opaque flap. In fact, in the absence of means for deflecting the light radiation from the emitters towards the receivers, no receiver ever receives light from an emitter. Thus, in this keyboard, keys are used which each control the positioning, at the intersection of a column and a line, of means for deflecting the light radiation from the corresponding emitter to the corresponding receiver. These deflection means are, in this case, formed by a reflecting surface slanted with respect to the propagation direction of the light in the column, so as to deflect a part of the light emitted through an angle of substantially 90.degree., in the direction of the line. So that the pressing of the key does not prevent light from passing through the channels, either a totally reflecting surface is used controlled by the key for insertion in a part only of the section of the propagation channel, or a semireflecting surface is used controlled by the key for insertion in the whole of the section of the propagation channel. In both cases, even if a key is pressed, it does not completely prevent light from passing, which means that keys pressed downstream, in the direction of propagation of the radiation, in the same column, or keys pressed upstream, in the same line, can be recognized.
A keyboard such as the one which has just been described, although it does not have the defects inherent in keyboards using light guides made from a transparent material having an index greater than that of air, has however other drawbacks. First of all, each of the keys, since it controls the positioning of a mobile reflectign surface whose slope angle must remain strictly constant, is mechanically more complicated than a key which controls the positioning of an opaque flap whose slope angle is not critical. Moreover, although the pressing of the key does not cause cancellation of the light downstream of this key, it causes attenuation thereof in relatively high proportions. This reduces the operating reliability of the keyboard and leads then also to the use of powerful sources and sensitive sensors.
The aim of the present invention is to overcome the preceding drawbacks.